Thin polymer films find extensive use in many areas. Capacitors employ low temperature thermoplastic dielectric thin film polymers, such as polypropylene (PP), polyethylene terephthalate (PET), polycarbonate, polyethylene-2,6-naphthalate, polyvinylidene difluoride (PVDF), polyphenylene oxide, and polyphenylene sulfide, either metallized or maintained between metal foil electrodes. Food packaging employs metallized polymer films, such as PP and PET, as a moisture barrier.
A monolithic capacitor is one in which the layers of electrodes and dielectric are bonded together in a unitary structure as opposed, for example, to a metallized film capacitor in which self-supporting films are rolled or wound into the capacitor form. A miniaturized capacitor is one of very small dimensions, so as to be suitable for microcircuitry.
Small overall size could denote low capacitance of little practical value, except that the thickness of the intervening dielectric layer inversely affects the capacitance between adjacent electrodes, and the number of electrode pairs directly affects capacitance. Therefore, as a matter of basic capacitor theory, a capacitor having very thin dielectric layers and many pairs of electrodes could have substantial capacitance despite being of miniature size, with the active area of the electrodes being quite small.
Metallized film capacitors are used extensively in a broad range of electrical and electronic equipment that include motor run and motor start circuits for air conditioners, fluorescent and high intensity light ballasts, power supplies, telecommunication equipment, instrumentation, and medical electronics. In many of these applications, the metallized capacitors are used to conserve energy by correcting the power factor of a circuit and in others they are used to perform specific functions, such as timing, filtering, and de-coupling. The advantages of metallized film over film foil capacitors include lower volume, weight, cost, and higher reliability due to the self-healing properties of the metallized films. The metallized polymer film dielectrics find use in such a multitude of high voltage and high frequency capacitor applications due to their low dielectric loss.
Such a miniaturized capacitor is disclosed and claimed in U.S. Pat. No. 5,018,048, issued May 21, 1991, to D. G. Shaw et al. While that capacitor is fine for its intended purpose, it tends to have a low breakdown strength, on the order of 150 Volts (V), compared to a theoretically possible higher breakdown strength on the order of 500 to 1000 V, depending on the configuration. The cause of the lower breakdown voltage appears to reside in exposed edges that arc over with increasing applied voltage.
Thus, a method of increasing the breakdown strength of miniaturized monolithic multi-layer capacitors is required.
With regard to food packaging, aluminum-coated thermoplastic polymer films are used to keep food fresh by acting as a barrier to air and water vapor. However, the aluminum film prevents visual inspection of the contents of the food package by the consumer. Market research has shown that consumers prefer to see inside the food package and view the condition of the contents.
Thus, a method of providing a window in food packaging is desired.